1. Field of Invention
This invention relates to modifiable displays with a plurality of stable display states and, more specifically, fixing regions of such modifiable displays to create displays with both fixed and changeable regions.
2. Description of Related Art
FIG. 1 shows one type of modifiable display with a plurality of stable display states. This type of modifiable display is a type of electric paper called the Gyricon. In FIG. 1, electric paper 1 consists of a polymer substrate 10 with elements 20 embedded that are one color, for example, white 30, on one side and another color, for example, black 40, on the other. Such electric paper is described in U.S. Pat. No. 5,604,027, incorporated herein by reference. Under the influence of an electric field, each element rotates so that either one colored side or the other is on top and, therefore, visible to a viewer viewing the electric paper from the top. The elements in this example have two stable states, but the elements can have more than two stable states. The stable state in which each element exists remains unchanged until the element is subjected to the electric field associated with a different stable state. In addition, the elements can be multicolored as discussed, for example, in U.S. Pat. No. 5,717,514, incorporated herein by reference, or cylindrical as discussed, for example, in pending U.S. patent application Ser. No. 08/960,865 entitled xe2x80x9cTWISTING CYLINDER DISPLAYxe2x80x9d filed Oct. 30, 1997, and pending U.S. patent application Ser. No. 08/960,868 entitled xe2x80x9cA TWISTING CYLINDER DISPLAY USING MULTIPLE CHROMATIC VALUESxe2x80x9d filed Oct. 30, 1997, incorporated herein by reference. FIG. 6 shows a cross sectional view of an example of electric paper. In FIG. 6, an element 20 is suspended in oil in a cavity 22 of elastomer 50. Elastomer 50 and element 20 are contained within an upper protective layer 60 and a lower protective layer 70. Because element 20 is suspended in oil within cavity 22, element 20 can freely rotate when subjected to an electric field.
Printing on this form of electric paper is accomplished by imposing an electrical pattern over the sheet, the electrical pattern being created by a voltage difference between the top side of the sheet and the bottom side of the sheet. As shown in U.S. Pat. No. 5,389,945, one way to do this is to pass the sheet under an imagewise charging bar. As the sheet passes under the bar, voltages are applied along a set of closely-spaced electrical contacts, one for each pixel or element.
While one kind of electric paper is described above, many kinds of electric paper are known. In addition, other kinds of modifiable displays such as, for example, electrophoretic displays (both single cell type and micro capsule type), thermally addressable displays, magnetically addressable displays and certain kinds of liquid crystal displays, are known.
While conventional electric paper is useful due to its ability to be erased and reused, its erasable property results in added steps being required to use the electric paper as a form (e.g., a form to be filled out by a user). In order to use conventional electric paper as a reusable form, after every erasure, the background or common portions of the form must be rewritten to the electric paper. This step of rewriting the background or common portions is necessary because these portions are erased along with the unique portions.
This problem is addressed by the invention by physically fixing a portion of the modifiable display that is common to all uses of that display such that normal erasure of the display will not erase the physically fixed portions. In the case of a form, the common portions could include, for example, grid lines, headings and labels such as xe2x80x9cNamexe2x80x9d for blocks to be filled in by a user of the form.
The present invention physically fixes selected regions of the display while leaving the remainder modifiable. The selected regions can be physically fixed in a number of ways. For example, the elements in the selected regions can be heated. By heating the selected regions, the elements in the selected regions can be disabled by, for example, applying an electrical field while the rotatable elements are heated above their melting temperatures, causing them to deform against the cavity wall and thus be no longer capable of rotation. Heating the selected regions can also cause chemical damage which can destroy the mechanisms by which the display operates. Still further damage can be effected by localized heating in which the local optical properties of the display material are changed by the introduction of changes in light absorption or scattering. An example of this is a decomposition of a hydrocarbon material in which a gas bubble is formed which causes scattering of incident light, or, in the case of the Gyricon, greatly interferes with the rotation of the balls. Fixing heat can be applied by using a laser, LED bar or the like. Pressure fixing can also be used to fix the selected regions by using an impact print head or bar to deform the elements or surrounding walls of the substrate. This will have the effect of damaging the rotatable elements, in the case of the Gyricon, and of, for example, destroying the alignment of the molecules at the window surfaces in the case of some liquid crystal kinds of electric paper.
Another aspect of the invention includes printing physically fixed information on the face of the display with standard marking technologies such as permanent ink pens, printers and photocopiers.
The physical fixing of the selected regions can be permanent or temporary. Methods for un-fixing previously fixed regions include removal of ink.